The hem flange joint is used to attach the inner and outer panels of almost all automotive closure assemblies (hoods, doors, trunk lids, lifigates). Typically, this mechanical lock joint is augmented with an adhesive, applied to the inner surface of one of the panels before assembly and hemming. There are many issues with this traditional assembly method, including adhesive cost, dispensing, cure time and cure initiation, closure stiffness and crashworthiness, and hem flange width requirements. One particular problem is relative sliding of the inner and outer panel after hemming and before the adhesive has cured. This results in poor panel fit on the body, as the outer skin has shifted relative to the attachment points on the inner panel. A possible solution to these problems is to laser tack weld the panels together shortly after hemming. Laser welding closure assemblies reduces the need for adhesive, and produces a stiffer, more robust assembly. It may be possible to reduce hem flange width for laser welded closures, and the panel shifting problem is eliminated once the assembly is welded. This paper will describe the process requirements for laser welding on a hem flange, a laser welding system designed for hem flange welding, and show hem flange welding results for both steel and aluminum closure assemblies.
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